Track assembly for providing traction to an off-road vehicle  such as an all-terrain vehicle (atv) or a snowmobile

ABSTRACT

A track assembly for traction of an off-road vehicle, such as an all-terrain vehicle (ATV) or a snowmobile, is disclosed. The track assembly comprises a plurality of track-contacting wheels, which comprises: a drive wheel; and a plurality of idler wheels spaced apart in a longitudinal direction of the track assembly. The track assembly also comprises an endless track disposed around the track-contacting wheels. A frame of the track assembly may comprise a hollow frame structure. The hollow frame structure may be dimensioned to impede accumulation of snow, mud, rocks, debris, etc. in the track assembly. The track assembly may comprise interwheel guides between longitudinally adjacent ones of the idler wheels to contact a bottom run of the endless track, and/or fenders adjacent to given ones of the idler wheels. The frame&#39;s hollowness, the interwheel guides, and/or the fenders may be realized during molding of a portion of the frame using a blow molding or other fluid-based molding process.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 USC 119(e) of U.S.Provisional Patent Application No. 61/409,354 filed on Nov. 2, 2010 andhereby incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates generally to off-road vehicles such as all-terrainvehicles (ATVs) and snowmobiles and, more particularly, to trackassemblies for providing traction to ATVs, snowmobiles and otheroff-road vehicles.

BACKGROUND

All-terrain vehicles (ATVs) used for recreational, utility and/or otherpurposes are sometimes provided with track assemblies having endlesstracks which engage the ground for traction. The track assemblies aremounted in place of ground-engaging wheels which would otherwise be usedfor traction in order to enhance the ATV's floatation and traction onthe ground.

A track assembly of an ATV typically comprises a frame, a plurality ofwheels, and an endless track disposed around the frame and the wheels toengage the ground. The endless track is driven around the frame and thewheels to generate traction. The frame supports various components ofthe track assembly, including some of the wheels.

While various designs of track assemblies have been developed for ATVs,they suffer from some drawbacks. For example, existing ATV trackassemblies may not be optimal for high-speed riding on trails or forriding in other situations or environments. Dynamics of an ATV maychange significantly because of the track assemblies' additional weightand configuration which are different from that of ground-engagingwheels with which the ATV may have been designed to be equipped. Also,during riding, the track assemblies tend to accumulate undesirableground matter (i.e., mud, rocks, soil, ice, snow, and/or other debris onthe ground) that increase their weight even more. Ride comfort is alsonot optimal in rough terrain because a track assembly's roller wheels,which roll on its endless track, engage the track only at limited areas,thereby potentially causing local deformation on the track that maycreate impacts and detrimentally affect ride comfort.

Track assemblies of snowmobiles and other off-road vehicles may sufferfrom similar and/or other drawbacks.

There thus remains a need to improve the performance of track assembliesfor ATVs, snowmobiles and other off-road vehicles.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a trackassembly for traction of an off-road vehicle. The track assemblycomprises a plurality of track-contacting wheels, which comprises: adrive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly. The track assembly alsocomprises an endless track disposed around the track-contacting wheelsand comprising an inner side facing the track-contacting wheels and aground-engaging outer side for engaging the ground. The drive wheel isrotatable to impart motion of the endless track. The idler wheelscontact a bottom run of the endless track. The track assembly alsocomprises a frame supporting the idler wheels. The frame comprises anonmetallic hollow frame structure.

According to another aspect of the invention, there is provided a trackassembly for traction of an off-road vehicle. The track assemblycomprises a plurality of track-contacting wheels, which comprises: adrive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly. The track assembly alsocomprises an endless track disposed around the track-contacting wheelsand comprising an inner side facing the track-contacting wheels and aground-engaging outer side for engaging the ground. The drive wheel isrotatable to impart motion of the endless track. The idler wheelscontact a bottom run of the endless track. The track assembly alsocomprises a frame supporting the idler wheels. The frame comprises ahollow frame structure. The hollow frame structure extends at least ashigh as a given one of the idler wheels such that a point of the hollowframe structure aligned with a top of the given one of the idler wheelsin the longitudinal direction of the track assembly is located at leastas high as the top of the given one of the idler wheels.

According to another aspect of the invention, there is provided a trackassembly for traction of an off-road vehicle. The track assemblycomprises a plurality of track-contacting wheels, which comprises: adrive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly. The track assembly alsocomprises an endless track disposed around the track-contacting wheelsand comprising an inner side facing the track-contacting wheels and aground-engaging outer side for engaging the ground. The drive wheel isrotatable to impart motion of the endless track. The idler wheelscontact a bottom run of the endless track. The track assembly alsocomprises a frame supporting the idler wheels. The frame comprises ahollow frame structure. The hollow frame structure has a cross-sectionalshape which changes along the longitudinal direction of the trackassembly.

According to another aspect of the invention, there is provided a trackassembly for traction of an off-road vehicle. The track assemblycomprises a plurality of track-contacting wheels, which comprises: adrive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly. The track assembly alsocomprises an endless track disposed around the track-contacting wheelsand comprising an inner side facing the track-contacting wheels and aground-engaging outer side for engaging the ground. The drive wheel isrotatable to impart motion of the endless track. The idler wheelscontact a bottom run of the endless track. The track assembly alsocomprises a frame supporting the idler wheels. The frame comprises ahollow frame structure. The hollow frame structure is shaped to impedeaccumulation of undesirable ground matter over the hollow framestructure.

According to another aspect of the invention, there is provided a trackassembly for traction of an off-road vehicle. The track assemblycomprises a plurality of track-contacting wheels, which comprises: adrive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly. The track assembly alsocomprises an endless track disposed around the track-contacting wheelsand comprising an inner side facing the track-contacting wheels and aground-engaging outer side for engaging the ground. The drive wheel isrotatable to impart motion of the endless track. The idler wheelscontact a bottom run of the endless track. The track assembly alsocomprises a frame supporting the idler wheels. The frame comprises ablow-molded hollow frame structure.

According to another aspect of the invention, there is provided a trackassembly for traction of an off-road vehicle. The track assemblycomprises a plurality of track-contacting wheels, which comprises: adrive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly. The track assembly alsocomprises an endless track disposed around the track-contacting wheelsand comprising an inner side facing the track-contacting wheels and aground-engaging outer side for engaging the ground. The drive wheel isrotatable to impart motion of the endless track. The idler wheelscontact a bottom run of the endless track. The track assembly alsocomprises an interwheel guide for contacting the bottom run of theendless track. The interwheel guide is located between a first one ofthe idler wheels and a second one of the idler wheels which are adjacentto one another in the longitudinal direction of the track assembly.

According to another aspect of the invention, there is provided a trackassembly for traction of an off-road vehicle. The track assemblycomprises a plurality of track-contacting wheels, which comprises: adrive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly. The track assembly alsocomprises an endless track disposed around the track-contacting wheelsand comprising an inner side facing the track-contacting wheels and aground-engaging outer side for engaging the ground. The drive wheel isrotatable to impart motion of the endless track. The idler wheelscontact a bottom run of the endless track. The track assembly alsocomprises a fender adjacent to a given one of the idler wheels.

According to another aspect of the invention, there is provided a trackassembly for traction of an off-road vehicle. The track assemblycomprises a plurality of track-contacting wheels, which comprises: adrive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly. The track assembly alsocomprises an endless track disposed around the track-contacting wheelsand comprising an inner side facing the track-contacting wheels and aground-engaging outer side for engaging the ground. The drive wheel isrotatable to impart motion of the endless track. The idler wheelscontact a bottom run of the endless track. The track assembly alsocomprises a deflector for deflecting undesirable ground mattertransported by the endless track to reduce undesirable ground matteraccumulation in the track assembly.

These and other aspects of the invention will now become apparent tothose of ordinary skill in the art upon review of the followingdescription of embodiments of the invention in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of embodiments of the invention is providedbelow, by way of example only, with reference to the accompanyingdrawings, in which:

FIGS. 1A and 1B show an example of an all-terrain vehicle (ATV)comprising track assemblies in accordance with an embodiment of theinvention;

FIGS. 2A and 2B show the ATV equipped with ground-engaging wheelsinstead of the track assemblies;

FIGS. 3 and 5 respectively show a perspective view and a side view of afront track assembly;

FIGS. 4 and 6 respectively show a perspective view and a side view of arear track assembly;

FIGS. 7, 9 and 10 respectively show a perspective view, a side view anda top view of the front track assembly without an endless track thereof;

FIGS. 8, 11 and 12 respectively show a perspective view, a side view anda top view of the rear track assembly without an endless track thereof;

FIG. 13 shows an end view of the rear track assembly;

FIGS. 14 and 15 respectively show a ground-engaging outer side and aninner side of a segment of an endless track;

FIGS. 16 and 18 respectively show a perspective view and a side view ofa frame of the front track assembly;

FIGS. 17 and 19 respectively show a perspective view and a side view ofa frame of the rear track assembly;

FIG. 20 shows a longitudinal sectional view of a lower frame structureof the frame;

FIGS. 21 and 22 respectively show different cross-sectional views of theframe;

FIG. 23 shows a bottom view of the front track assembly without itsendless track;

FIG. 24 shows a perspective view showing an interconnection of an upperframe structure and a lower frame structure of the frame;

FIG. 25 is a flowchart illustrating an example of a blow-molding processused to mold the lower frame structure; and

FIG. 26 shows an example of a snowmobile comprising a track assembly inaccordance with another embodiment of the invention.

It is to be expressly understood that the description and drawings areonly for the purpose of illustrating certain embodiments of theinvention and are an aid for understanding. They are not intended to bea definition of the limits of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an all-terrain vehicle (ATV) 10 in accordance with anembodiment of the invention. The ATV 10 is a small open vehicle designedto travel off-road on a variety of terrains, including roadless ruggedterrain, for recreational, utility and/or other purposes.

In this embodiment, the ATV 10 comprises a prime mover 12, a pluralityof track assemblies 16 ₁-16 ₄, a seat 18, and a user interface 20, whichenable a user of the ATV to ride the ATV 10 on the ground.

The prime mover 12 is a source of motive power that comprises one ormore motors. For example, in this embodiment, the prime mover 12comprises an internal combustion engine. In other embodiments, the primemover 12 may comprise another type of motor (e.g., an electric motor) ora combination of different types of motor (e.g., an internal combustionengine and an electric motor).

The prime mover 12 is in a driving relationship with one or more of thetrack assemblies 16 ₁-16 ₄. That is, motive power generated by the primemover 12 is transmitted to one or more of the track assemblies 16 ₁-16 ₂via a powertrain of the ATV 10 (e.g., via a transmission and adifferential of the powertrain).

In this case, the seat 18 is a straddle seat and the ATV 10 is usable bya single person such that the seat 18 accommodates only that persondriving the ATV 10. In other cases, the seat 18 may be another type ofseat, and/or the ATV 10 may be usable by two individuals, namely oneperson driving the ATV 10 and a passenger, such that the seat 18 mayaccommodate both of these individuals (e.g., behind one another orside-by-side) or the ATV 10 may comprise an additional seat for thepassenger. For example, in other embodiments, the ATV 10 may be aside-by-side ATV, sometimes referred to as a “utility terrain vehicle”or “UTV”.

The user interface 20 allows the user to interact with the ATV 10. Moreparticularly, the user interface 20 comprises an accelerator, a brakecontrol, and a steering device that are operated by the user to controlmotion of the ATV 10 on the ground. In this case, the steering devicecomprises handlebars. In other cases, the steering device may comprise asteering wheel or other type of steering element. The user interface 20also comprises an instrument panel (e.g., a dashboard) which providesindicators (e.g., a speedometer indicator, a tachometer indicator, etc.)to convey information to the user.

The track assemblies 16 ₁-16 ₄ engage the ground to provide traction tothe ATV 10. More particularly, in this example, front ones of the trackassemblies 16 ₁-16 ₄ provide front traction to the ATV 10 while rearones of the track assemblies 16 ₁-16 ₄ provide rear traction to the ATV10. Each of the front ones of the track assemblies 16 ₁-16 ₄ ispivotable about a steering axis of the ATV 10 in response to input ofthe user at the handlebars in order to steer the ATV 10 on the ground.

In this embodiment, each track assembly 16 _(i) is mounted in place of aground-engaging wheel that may otherwise be mounted at a position of thetrack assembly 16 _(i) to propel the ATV 10 on the ground. For example,as shown in FIG. 2, the ATV 10 may be propelled on the ground by fourground-engaging wheels 15 ₁-15 ₄ with tires instead of the trackassemblies 16 ₁-16 ₄. Basically, in this embodiment, the trackassemblies 16 ₁-16 ₄ may be used to convert the ATV 10 from a wheeledvehicle into a tracked vehicle, thereby enhancing its traction andfloatation on the ground.

With additional reference to FIGS. 3 to 13, in this embodiment, eachtrack assembly 16 _(i) comprises a frame 44, a plurality oftrack-contacting wheels including a drive wheel 42 and a plurality ofidler wheels 50 ₁-50 ₁₀, and an endless track 41 disposed around theframe 44 and the wheels 42, 50 ₁-50 ₁₀. The track assembly 16 _(i) has afront longitudinal end 57 and a rear longitudinal end 59 that define alength of the track assembly 16 _(i). A width of the track assembly 16_(i) is defined by a width of the endless track 41. The track assembly16 _(i) has a longitudinal direction, transversal directions including awidthwise direction, and a height direction.

The endless track 41 engages the ground to provide traction to the ATV10. The track 41 has an inner side 45 facing the wheels 42, 50 ₁-50 ₁₀and defining an inner area of the track 41 in which these wheels arelocated. The track 41 also has a ground-engaging outer side 47 oppositethe inner side 45 for engaging the ground on which the ATV 10 travels.The endless track 41 has a top run 65 which extends between thelongitudinal ends 57, 59 of the track assembly 16 _(i) and over thedrive wheel 42, and a bottom run 66 which extends between thelongitudinal ends 57, 59 of the track assembly 16 _(i) and under theidler wheels 50 ₁-50 ₁₀. The endless track 41 has a longitudinaldirection, transversal directions including a widthwise direction, and athickness direction.

With additional reference to FIGS. 14 and 15, the endless track 41comprises a body 36 underlying its inner side 45 and its ground-engagingouter side 47. In view of its underlying nature, the body 36 can bereferred to as a “carcass”. In this embodiment, the body 36 is anelastomeric body in that it comprises elastomeric material which allowsthe track 41 to elastically change in shape as it is in motion aroundthe wheels 42, 50 ₁-50 ₁₀. The elastomeric material of the carcass 36can be any polymeric material with suitable elasticity. In thisembodiment, the elastomeric material includes rubber. Various rubbercompounds may be used and, in some cases, different rubber compounds maybe present in different areas of the carcass 36. In other embodiments,the elastomeric material of the carcass 36 may include another elastomerin addition to or instead of rubber (e.g., polyurethane elastomer).

Also, in this embodiment, the carcass 36 comprises a plurality ofreinforcements embedded in its elastomeric material 38. One example of areinforcement is a layer of reinforcing cables that are adjacent to oneanother and that extend in the longitudinal direction of the track 41 toenhance strength in tension of the track 41 along its longitudinaldirection. In some cases, a reinforcing cable may be a cord or wire ropeincluding a plurality of strands or wires. In other cases, a reinforcingcable may be another type of cable and may be made of any materialsuitably flexible longitudinally (e.g., fibers or wires of metal,plastic or composite material). Another example of a reinforcement is alayer of reinforcing fabric. Reinforcing fabric comprises pliablematerial made usually by weaving, felting, or knitting natural orsynthetic fibers. For instance, a layer of reinforcing fabric maycomprise a ply of reinforcing woven fibers (e.g., nylon fibers or othersynthetic fibers). Various other types of reinforcements may be providedin the carcass 36 in other embodiments.

In this embodiment, the inner side 45 of the endless track 41 comprisesa plurality of inner projections 48 ₁-48 _(N) that contact at least someof the wheels 42, 50 ₁-50 ₁₀ and that are used to do at least one ofdriving (i.e., imparting motion to) the track 41 and guiding the track41. In that sense, the inner projections 48 ₁-48 _(N) can be referred toas “drive/guide projections”, meaning that each drive/guide projectionis used to do at least one of driving the track 41 and guiding the track41. Also, such drive/guide projections are sometimes referred to as“drive/guide lugs” and will thus be referred to as such herein. Moreparticularly, in this embodiment, the drive/guide lugs 48 ₁-48 _(N)interact with the drive wheel 42 in order to cause the track 41 to bedriven, and also interact with the idler wheels 50 ₁-50 ₁₀ in order toguide the track 41 as it is driven by the drive wheel 42. Thedrive/guide lugs 48 ₁-48 _(N) are thus used to both drive the track 41and guide the track 41 in this embodiment.

The drive/guide lugs 48 ₁-48 _(N) are spaced apart along thelongitudinal direction of the endless track 41. In this case, thedrive/guide lugs 48 ₁-48 _(N) are arranged in a plurality of rows thatare spaced apart along the widthwise direction of the endless track 41.The drive/guide lugs 48 ₁-48 _(N) may be arranged in other manners inother embodiments.

In this example, each drive/guide lug 48 _(i) is an elastomericdrive/guide lug in that it comprises elastomeric material. Theelastomeric material of the drive/guide lug 48 _(i) can be any polymericmaterial with suitable elasticity. More particularly, in this case, theelastomeric material of the drive/guide lug 48 _(i) includes rubber.Various rubber compounds may be used and, in some cases, differentrubber compounds may be present in different areas of the drive/guidelug 48 _(i). In other cases, the elastomeric material of the drive/guidelug 48 _(i) may include another elastomer in addition to or instead ofrubber.

The ground-engaging outer side 47 comprises a plurality of tractionprojections 61 ₁-61 _(m) (sometimes referred to as “traction lugs” or“traction profiles”) that engage and may penetrate into the ground toenhance traction. The traction lugs 61 ₁-61 _(m) are spaced apart alongthe longitudinal direction of the track assembly 16 _(i).

In this example, each traction lug 61 _(i) is an elastomeric tractionlug in that it comprises elastomeric material. The elastomeric materialof the traction lug 61 _(i) can be any polymeric material with suitableelasticity. More particularly, in this case, the elastomeric material ofthe traction lug 61 _(i) includes rubber. Various rubber compounds maybe used and, in some cases, different rubber compounds may be present indifferent areas of the traction lug 61 _(i). In other cases, theelastomeric material of the traction lug 61 _(i) may include anotherelastomer in addition to or instead of rubber.

The endless track 41 may be constructed in various other manners inother embodiments. For example, in some embodiments, the track 41 maycomprise a plurality of parts (e.g., rubber sections) interconnected toone another to form an endless belt, the track 41 may have recesses orholes that interact with the drive wheel 42 in order to cause the track41 to be driven (e.g., in which case the drive/guide lugs 48 ₁-48 _(N)may be used only to guide the track 41 without being used to drive thetrack 41), and/or the ground-engaging outer side 47 of the track 41 maycomprise various patterns of traction projections.

The drive wheel 42 is rotatable about an axis of rotation 49 for drivingthe endless track 41. The axis of rotation 49 corresponds to an axle ofthe ATV 10. More particularly, in this example, the drive wheel 42 has ahub which is mounted to the axle of the ATV 10 such that power generatedby the prime mover 12 and delivered over the powertrain of the ATV 10rotates the axle, which rotates the drive wheel 42, which imparts motionof the track 41. In this embodiment in which the track assembly 16 _(i)is mounted where a ground-engaging wheel 15 _(i) could otherwise bemounted, the axle of the ATV 10 is capable of rotating the drive wheel42 of the track assembly 16 _(i) or the ground-engaging wheel 15 _(i).

In this embodiment, the drive wheel 42 comprises a drive sprocketengaging the drive/guide lugs 48 ₁-48 _(N) of the inner side 45 of thetrack 41 in order to drive the track 41. In this case, the drivesprocket 42 comprises a plurality of teeth 46 ₁-46 _(T) distributedcircumferentially along its rim and projecting axially along its axis ofrotation 49 to define a plurality of lug-receiving spaces 40 ₁-40 _(S)therebetween that receive the drive/guide lugs 48 ₁-48 _(N) of the track41. The drive wheel 42 may be configured in various other ways in otherembodiments. For example, in embodiments where the track 41 comprisesrecesses or holes, the drive wheel 42 may have teeth that enter theserecesses or holes in order to drive the track 41. As yet anotherexample, in some embodiments, the drive wheel 42 may frictionally engagethe inner side 45 of the track 41 in order to frictionally drive thetrack 41.

The idler wheels 50 ₁-50 ₁₀ are not driven by power supplied by theprime mover 12, but are rather used to do at least one of supportingpart of the weight of the ATV 10 on the ground via the track 41, guidingthe track 41 as it is driven by the drive wheel 42, and tensioning thetrack 41. More particularly, in this embodiment, the idler wheels 50 ₁,50 ₂ and the idler wheels 50 ₉, 50 ₁₀ are respectively front idlerwheels (leading idler wheels) and rear idler wheels (trailing idlerwheels) that maintain the track 41 in tension, and can help to supportpart of the weight of the ATV 10 on the ground via the track 41. Theidler wheels 50 ₃-50 ₈ are roller wheels that roll on the inner side 45of the track 41 along the bottom run 66 of the track 41 to apply thebottom run 66 on the ground. The idler wheels 50 ₁-50 ₁₀ may be arrangedin other configurations and/or the track assembly 16 _(i) may comprisemore or less idler wheels in other embodiments.

The frame 44 supports components of the track assembly 16 _(i),including the idler wheels 50 ₁-50 ₁₀. More particularly, in thisembodiment, the front idler wheels 50 _(i), 50 ₂ are mounted to theframe 44 in a front longitudinal end region of the frame 44 proximatethe front longitudinal end 57 of the track assembly 16 _(i), with eachof these front idler wheels being located on a respective one of a firstlateral side 30 ₁ and a second lateral side 30 ₂ of the frame 44. Therear idler wheels 50 ₉, 50 ₁₀ are mounted to the frame 44 in a rearlongitudinal end region of the frame 44 proximate the rear longitudinalend 59 of the track assembly 16 _(i), with each of these rear idlerwheels being located on a respective one of the lateral sides 30 ₁, 30 ₂of the frame 44. The roller wheels 50 ₃-50 ₈ are mounted to the frame 44in a central region of the frame 44 between the front idler wheels 50 ₁,50 ₂ and the rear idler wheels 50 ₉, 50 ₁₀. The roller wheels 50 ₃-50 ₅are located on the lateral side 30 ₁ of the frame 44, while the rollerwheels 50 ₆-50 ₈ are located on the lateral side 30 ₂ of the frame 44.Each of the roller wheels 50 ₃-50 ₈ may be rotatably mounted directly tothe frame 44 or may be rotatably mounted to a link which is pivotallymounted to the frame 44 to which is rotatably mounted an adjacent one ofthe roller wheels 50 ₃-50 ₈, thus forming a “tandem”. For instance, inthis case, the roller wheel 50 ₃ is rotatably mounted directly to theframe 44, while the roller wheels 50 ₄, 50 ₅ are rotatably mounted to alink 17 that is pivotally mounted to the frame 44 such that the rollerwheels 50 ₄, 50 ₅ and their link 17 can pivot in tandem relative to theframe 44.

The frame 44 is supported at a support area 39. More specifically, inthis case, the frame 44 is supported by the axle of the ATV 10 to whichis coupled the drive wheel 42, such that the support area 39 isintersected by the axis of rotation 49 of the drive wheel 42.

In this embodiment, the frame 44 is pivotable about a pivot axis 51 tofacilitate motion of the track assembly 16 _(i) on uneven terrain andenhance its traction on the ground. More particularly, in thisembodiment, the pivot axis 51 corresponds to the axis of rotation 49 ofthe drive wheel 42 and the frame 44 can pivot about the axle of the ATV10 to which the drive wheel 42 is coupled. In other embodiments, thepivot axis 51 of the frame 44 may be located elsewhere (e.g., lower)than the axis of rotation 49 of the drive wheel 42. In yet otherembodiments, the frame 44 may not be pivotable.

Also, in this embodiment, the track assembly 16 _(i) comprises ananti-rotation connector 52 to limit a pivoting movement of the trackassembly 16 _(i) relative to a chassis of the ATV 10. In this example,the anti-rotation connector 52 comprises a spring and a damper and isconnected between the frame 44 of the track assembly 16 _(i) and thechassis of the ATV 10 (e.g., via one or more mounting brackets and/orfasteners).

With additional reference to FIGS. 16 to 19, in this embodiment, theframe 44 comprises a lower frame structure 60 and an upper framestructure 62 extending upwardly from the lower frame structure 60.

The lower frame structure 60 defines a front longitudinal end 63 and arear longitudinal end 64 of the frame 44. That is, the lower framestructure 60 has a length which extends from the front longitudinal end63 to the rear longitudinal end 64 of the frame 44. The lower framestructure 60 forms a frame base. In this case, the lower frame structure60 supports the idler wheels 50 ₁-50 ₁₀ and therefore forms awheel-supporting frame base.

In this embodiment, the lower frame structure 60 comprises a pluralityof surfaces, including a top surface 71 ₁, a bottom surface 71 ₂, and apair of lateral surfaces 71 ₃, 71 ₄ opposite one another. The topsurface 71 ₁ faces the drive wheel 42, the bottom surface 71 ₂ faces thebottom run 66 of the endless track 41, and the lateral surfaces 71 ₃, 71₄ face respective ones of the idler wheels 50 ₁-50 ₁₀.

In this embodiment, the lower frame structure 60 is relativelyvoluminous and occupies a significant space within the track assembly 16_(i) in order to impede accumulation of unwanted ground matter (i.e.,mud, rocks, soil, ice, snow, and/or other debris on the ground) withinthe track assembly 16 _(i), while remaining lightweight. In addition, inthis embodiment, the lower frame structure 60 is configured to providevarious structural features (e.g., guides for the endless track 41)enhancing performance of the track assembly 16 _(i).

For example, in this embodiment, the lower frame structure 60 extendsrelatively high within the track assembly 16 _(i). For instance, in thisembodiment, the lower frame structure 60 extends at least as high, andin some cases higher, than some of the idler wheels 50 ₁-50 ₁₀. Thelower frame structure 60 extends as high or higher than an idler wheel50 _(i) if a point of the lower frame structure 60 aligned with a top ofthe idler wheel 50 _(i) in the longitudinal direction of the trackassembly 16 _(i) is located as high or higher than the top of the idlerwheel 50 _(i). For example, in this embodiment, the lower framestructure 60 extends as high as the roller wheel 50 ₅ and higher thanthe roller wheels 50 ₃, 50 ₄, 50 ₆, 50 ₇.

Also, in this embodiment, a cross-sectional shape of the lower framestructure 60 changes along the longitudinal direction of the trackassembly 16 _(i). For example, in this embodiment, a height of thecross-sectional shape of the lower frame structure 60 (measured in theheight direction of the track assembly 16 _(i)) varies along thelongitudinal direction of the track assembly 16 _(i). In addition, inthis embodiment, a width of the cross-sectional shape of the lower framestructure 60 (measured in the widthwise direction of the track assembly16 _(i)) varies along the longitudinal direction of the track assembly16 _(i).

For instance, in this embodiment, the cross-sectional shape of the lowerframe structure 60 varies such that the top surface 71 ₁ of the lowerframe structure 60 is concave to conform to the drive wheel 42. This mayallow a gap between the top surface 71 ₁ of the lower frame structure 60and the drive wheel 42 to be minimized. This also allows the lower framestructure 60 to extend as high or higher than some of the idler wheelsidler wheels 50 ₁-50 ₁₀, as discussed above. Also, in this embodiment,the cross-sectional shape of the lower frame structure 60 varies suchthat the bottom surface 71 ₂ and the lateral surfaces 71 ₃, 71 ₄ of thelower frame structure 60 form structural features (e.g., guides for theendless track 41), as will be further discussed later on.

The upper frame structure 62 extends upwardly from the lower framestructure 60 to a top of the frame 44. Thus, the upper frame structure62 extends between the lower frame structure 60 and the support area 39,and in this case the pivot axis 51, of the frame 44. Along thelongitudinal direction of the track assembly 16 _(i), the upper framestructure 62 is shorter than the lower frame structure 60. In thisembodiment, the upper frame structure 62 forms an upper frame linkbetween the support area 39 of the frame 44 and the wheel-supportingframe base formed by the lower frame structure 60. More particularly, inthis embodiment, the upper frame structure 62 comprises a pair of framemembers 67 ₁, 67 ₂ that are angled relative to one another and convergeupwardly, in this case towards the pivot axis 51 of the frame 44, givingto the upper frame structure 62 a generally triangular or invertedV-shaped configuration.

The frame 44 is made one or more materials providing strength andrigidity to the frame 44. A material making up a portion of the frame 44is one which imparts strength and rigidity to that portion of the frame44. In some cases, a single material may make up an entirety of theframe 44. In other cases, different materials may make up differentportions of the frame 44.

In this embodiment, the lower frame structure 60 is a nonmetallic framestructure. The lower frame structure 60 is nonmetallic in that it is atleast mainly (i.e., it is mostly or entirely) made of nonmetal. That is,nonmetal is a sole or main constituent of the lower frame structure 60.Metal is not a main constituent of the lower frame structure 60.

More particularly, in this embodiment, the lower frame structure 60 is apolymeric frame structure. The lower frame structure 60 is polymeric inthat it is at least mainly (i.e., it is mostly or entirely) made ofpolymer. In some cases, the polymeric lower frame structure 60 mayinclude a single polymer. In other cases, the polymeric lower framestructure 60 may include a combination of polymers. In yet other cases,the polymeric lower frame structure 60 may include a polymer-matrixcomposite comprising a polymer matrix in which reinforcements areembedded (e.g., a fiber-reinforced polymer such as acarbon-fiber-reinforced polymer or glass-fiber-reinforced polymer). Inthis example of implementation, the polymeric lower frame structure 60includes high-density polyethylene. Any other suitable polymer may beused in other examples of implementation (e.g., polypropylene,polyurethane, polycarbonate, low-density polyethylene, nylon, etc.).

With additional reference to FIGS. 20 to 22, in this embodiment, thelower frame structure 60 is a hollow frame structure. That is, the lowerframe structure 60 comprises a hollow interior 68. More particularly, inthis embodiment, the hollow interior 68 occupies a majority of a volumeof the lower frame structure 60. The hollow interior 68 thereforeoccupies at least 50%, in some cases at least 65%, in some cases atleast 80%, and in some cases an even greater proportion of the volume ofthe lower frame structure 60. In other embodiments, the hollow interior68 may occupy a smaller proportion of the volume of the lower framestructure 60. This hollowness of the lower frame structure 60 helps toreduce a weight of the frame 44. In this case, as further discussedlater, the hollowness of the lower frame structure 60 is created duringmolding of the lower frame structure 60.

The hollow interior 68 is defined by a wall 29 of the lower framestructure 60. The wall 29 encloses the hollow interior 68 such that thehollow interior 68 is closed. This prevents mud, rocks, debris and/orother undesirable ground matter from entering into the hollow interior68 of the lower frame structure 60.

The wall 29 has a thickness suitable for providing sufficient rigidityto the lower frame structure 60. This depends on the material making upthe lower frame structure 60 and on loads to which the lower framestructure 60 is expected to be subjected to. For example, in someembodiments, the thickness of the wall 29 may be at least 1 mm, in somecases at least 2 mm, in some cases at least 3 mm, and in some cases atleast 4 mm. For instance, in this example of implementation in which thewall 29 includes high-density polyethylene, the thickness of the wall 29may be between 1 mm and 5 mm. In cases in which the thickness of thewall 29 varies such that it takes on different values in differentregions of the lower frame structure 60, the thickness of the wall 29may be taken as its minimum thickness. In other cases, the thickness ofthe wall 29 may be generally constant over an entirety of the lowerframe structure 60.

In this embodiment, the track assembly 16 _(i) comprises a plurality ofinterwheel guides 70 ₁-70 ₄ for contacting the endless track 41 duringuse to maintain a desired shape of the track 41. More particularly, inthis embodiment, the interwheel guides 70 ₁-70 are disposed to come intocontact with the bottom run 66 of the track 41 during use (e.g., whenthe bottom run 66 of the track 41 engages a rock, bump, etc., on theground), thereby forming “bumpers” or “abutments” against which thebottom run 66 of the track 41 may abut. Each interwheel guide 70 _(i) islocated between adjacent ones of the idler wheels 50 ₁-50 ₁₀ which areadjacent to one another along the longitudinal direction of trackassembly 16 _(i). By contacting a given section of the endless track 41that is between the adjacent ones of the idler wheels 50 ₁-50 ₁₀ betweenwhich it is located, the interwheel guide 70 _(i) helps to maintain adesired shape of the given section of the track 41 by countering atendency of the given section of the track 41 to curve inwardly in a gapthat would otherwise exist between these adjacent ones of the idlerwheels if the interwheel guide 70 _(i) was omitted (e.g., when the givensection of the track 41 bears against a rock, a bump, etc., on theground). Also, in this embodiment, when the track assembly 16 _(i)experiences large lateral forces, the interwheel guides 70 ₁-70 ₄ maycontact some of the drive/guide lugs 48 ₁-48 _(N) to oppose a tendencyof the track 41 to detrack laterally. In addition, in this embodiment,when a lateral edge portion of the track 41 tends to bend inwardly(e.g., due to a rock, a bump, etc., on the ground), the interwheelguides 70 ₁-70 ₄ may prevent the lateral edge portion of the track 41from bending to such a degree that it engages lateral faces of some ofthe idler wheels 50 ₁-50 ₁₀. As further discussed later, in thisembodiment, the interwheel guides 70 ₁-70 ₄ are integrally formed withthe lower frame structure 60 during molding of the lower frame structure60.

More particularly, in this embodiment, the interwheel guide 70 ₁ islocated between the front idler wheel 50 ₁ and the roller wheel 50 ₃ andcomprises a track-contacting surface 72 to contact the endless track 41during use. With additional reference to FIG. 23, in this case, thetrack-contacting surface 72 has a point P_(s) located, along thewidthwise direction of the track assembly 16 _(i), where a point P_(w)of a circumferential surface 74 of each of the front idler wheel 50 ₁and the roller wheel 50 ₃ is located. Also, in this case, thetrack-contacting surface 72 is generally parallel to a line T tangent tothe front idler wheel 50 ₁ and the roller wheel 50 ₃. This creates aguiding effect which acts to maintain a desired shape of a section 53 ofthe endless track 41 between the front idler wheel 50 ₁ and the rollerwheel 50 ₃. More specifically, in this example, the shape of the section53 of the endless track 41 is maintained such that the section 53 of theendless track 41 remains generally parallel to the line T tangent to thefront idler wheel 50 ₁ and the roller wheel 50 ₃.

The interwheel guides 70 ₂-70 ₄ are configured in a manner similar tothat described above in respect of the interwheel guide 70 ₁.

Each of the interwheel guides 70 ₁-70 ₄ may be configured in variousother ways in other embodiments. For example, in some embodiments, thetrack-contacting surface 72 of an interwheel guide 70 ₁ may not beparallel to the line T tangent to the adjacent ones of the idler wheels50 ₁-50 ₁₀ between which the interwheel guide 70 _(i) is located.

In this embodiment, the track assembly 16 _(i) comprises a plurality offenders 80 ₁-80 ₈ adjacent to respective ones of the idler wheels 50₁-50 ₈. The fenders 80 ₁-80 ₈ may help to protect against large rocks orother ground objects becoming trapped into the track assembly 16 i(e.g., between the frame 44 and an idler wheel 50 _(i), between theframe 44 and the drive wheel 42, between the frame 44 and the endlesstrack 41, and/or between any other moving and static components of thetrack assembly 16 _(i)). In addition, in this case, the fenders 80 ₁-80₈ occupy space within the track assembly 16 _(i) which would otherwise(i.e., if they were omitted) be available for unwanted ground matter toaccumulate in. In this embodiment, a fender 80 _(i) may be contiguous toan interwheel guide 70 _(i) (e.g., the fender 80 ₂ is contiguous to theinterwheel guide 70 ₁) or may not be contiguous to any of the interwheelguides 70 ₁-70 ₄ (e.g., the fender 80 ₃ is not contiguous to any of theinterwheel guides 70 ₁-70 ₄). As further discussed later, in thisembodiment, the fenders 80 ₁-80 ₈ are integrally formed with the lowerframe structure 60 during molding of the lower frame structure 60.

More particularly, in this embodiment, the fender 80 ₃ is adjacent tothe roller wheel 50 ₃. The fender 80 ₃ is configured to generallyconform to a contour of the roller wheel 50 ₃. Basically, the fender 80₃ has a wheel-facing surface 81 that faces the roller wheel 50 ₃ andthat is concave to accommodate the contour of the roller wheel 50 ₃. Inthis case, the wheel-facing surface 81 of the fender 80 ₃ is curved togenerally conform to the contour of the roller wheel 50 ₃. In othercases, the wheel-facing surface 81 of the fender 80 ₃ may have one ormore straight segments and/or one or more curved segments arranged togenerally conform to the contour of the roller wheel 50 ₃.

A gap between the wheel-facing surface 81 of the fender 80 ₃ and theroller wheel 50 ₃ may be dimensioned to prevent entry into the gap oflarge rocks, which, if trapped in the track assembly 16 _(i), could beproblematic. For example, in some embodiments, the gap may have a size(e.g., 5 mm or any other suitable size) which corresponds to a size of arock which is considered to be insufficient to block the roller wheel 50₃ if it were to enter through the gap. In some cases, the gap may varyin size along the fender 80 ₃ (e.g, increase from 5 mm to 6 mm and thento 7 mm near a center of the roller wheel 50 ₃). For instance, anincrease in size of the gap may facilitate egress of smaller rocks whichwould enter the gap. In such cases, the size of the gap can be taken asa minimum value of the size of the gap.

The fenders 80 ₁, 80 ₂, 80 ₄-80 ₈ are configured in a manner similar tothat described above in respect of the fenders 80 ₂, 80 ₃.

Each of the fenders 80 ₁-80 ₈ may be configured in various other ways inother embodiments. For example, in some embodiments, each of the fenders80 ₁-80 ₈ may have various other shapes that follow a greater or lesserpart of the contour of a respective one of the idler wheels 50 ₁-50 ₈ towhich it is adjacent.

In this embodiment, the lower frame structure 60 also comprises adeflector 75 for deflecting unwanted ground matter which would enter thetrack assembly 16 _(i) in order to reduce unwanted ground matteraccumulation in the track assembly 16 _(i). For example, in some cases,unwanted ground matter may be transported by the endless track 41 (e.g.,by the drive/guide lugs 48 ₁-48 _(N)) and, as it reaches the rear regionof the track assembly 16 _(i) where the track 41 turns about the rearidler wheels 50 ₁, 50 ₉, it may fall from the track 41 and be deflectedoutside of the track assembly 16 _(i) by the deflector 75. In thisembodiment, the deflector 75 includes a deflecting surface 76 which isoriented so as to deflect unwanted ground matter towards the lateralsides of the track assembly 16 _(i). More particularly, in this example,the deflecting surface 76 includes two opposite surface portions thatdiverge from one another downwardly to facilitate deflection of unwantedground matter towards the lateral sides of the track assembly 16 _(i).The deflector 75 may be configured in various other ways in otherembodiments.

The lower frame structure 60 may be manufactured in various manners. Inthis embodiment, the lower frame structure 60 is molded into shape suchthat it is a molded frame structure. In particular, in this case, thehollowness, the interwheel guides 70 ₁-70 ₄ and the fenders 80 ₁-80 ₈ ofthe lower frame structure 60 are realized during molding of the lowerframe structure 60.

More specifically, in this embodiment, the lower frame structure 60 isblow-molded into shape such that it is a blow-molded frame structure.For instance, FIG. 25 is a flowchart illustrating an example of ablow-molding process used to mold the lower frame structure 60.

At step 200, polymeric material that will make up the lower framestructure 60 is provided. For instance, in some cases, the polymericmaterial may be provided as a preform (also sometimes called “parison”),which is essentially a hot hollow tube of polymeric material. In othercases, the polymeric material may be provided as one or more hot sheets.

At step 220, pressurized gas (e.g., compressed air) is used to expandthe polymeric material against a mold. The mold has an internal shapegenerally corresponding to the shape of the lower frame structure 60such that, as it is expanded against the mold, the polymeric material isshaped into the lower frame structure 60. In this embodiment, thiscreates the hollow interior space 68, the interwheel guides 70 ₁-70 ₄and the fenders 80 ₁-80 ₈ of the lower frame structure 60. Pressure isheld until the polymeric material cools and hardens.

At step 240, once the polymeric material has cooled and hardened, thelower frame structure 60 is retrieved from the mold.

At optional step 260, one or more additional operations (e.g., trimming)may be performed on the lower frame structure 60 which has been molded.

In this embodiment, the upper frame structure 62 is a metallic framestructure. Strength and rigidity of the metallic material making up theupper frame structure 62 makes the upper frame structure 62, includingthe support area 39 of the frame 44 (at the axle of the ATV 10 to whichis coupled the drive wheel 42), strong and rigid. In particular, in thisembodiment, the upper frame structure 62 is more rigid than the lowerframe structure 60.

More particularly, in this example of implementation, the metallicmaterial making up the upper frame structure 62 includes aluminum. Thisprovides strength and rigidity to the upper frame structure 62 whilekeeping it lightweight. Any other suitable metal may be used in otherexamples of implementation (e.g., steel). In this case, the upper framestructure 62 is cast into shape. The upper frame structure 62 may bemanufactured using other techniques in other cases (e.g., machining,welding, etc.).

In this embodiment, the anti-rotation connector 52 is mounted to theupper frame structure 62. Strength and rigidity of the metallic materialmaking up the upper frame structure 62 provides a strong and rigidmounting point for the anti-rotation connector 62. In other embodiments,the anti-rotation connector 52 may be mounted to the lower framestructure 60.

Since they are separately made in this embodiment, the upper framestructure 62 and the lower frame structure 60 are secured to oneanother. More particularly, in this embodiment, as shown in FIG. 24, theupper frame structure 62 and the lower frame structure 60 are fastenedto one another by a plurality of fasteners 82 ₁-82 _(F) (e.g., bolts,screws, etc.). In this case, the upper frame structure 62 and the lowerframe structure 60 are connected to one another such that they remainimmobile relative to one another during use. In other cases, the upperframe structure 62 and the lower frame structure 60 may be connected toone another such that they are movable (e.g., pivotable) relative to oneanother during use.

As shown in FIG. 23, in this embodiment, the track assembly 16 _(i)comprises a bottom slider 56 facing the bottom surface 71 ₂ of the lowerframe structure 60 to slide against the endless track 41 during use.

More particularly, in this embodiment, the bottom slider 56 is separatefrom and removably mounted to the frame 44. In other words, the bottomslider 56 is a removable bottom slider. Specifically, in this case, thebottom slider 56 is fastened to the frame 44 by fasteners 58 ₁-58 ₄.This allows the bottom slider 56 to be removed and possibly replaced bya new bottom slider, for instance, when the bottom slider 56 is worn outor damaged. The bottom slider 56 may have a low coefficient of frictionwith the endless track 41 and suitable wear resistance. For example, inthis embodiment, the bottom slider 56 is at least partly made ofpolymeric material. In this example of implementation, the polymericmaterial of the bottom slider 56 includes high-density polyethylene. Anyother suitable polymer may be used in other examples of implementation(e.g., low-density polyethylene, nylon, etc.).

In this embodiment, the bottom surface 71 ₂ of the lower frame structure60 includes a front track-contacting projection 73 ₁ and a reartrack-contacting projection 73 ₂ that are aligned with the bottom slider56. The track-contacting projections 73 ₁, 73 ₂ act as front and rearbottom sliders, assist in retaining the bottom slider 56 in place, andlimit the length of the bottom slider 56 which may need to be replacedwhen worn out or damaged. In this case, the track-contacting projections73 ₁, 73 ₂ are formed during molding of the lower frame structure 60.

In other embodiments, the bottom slider 56 may be formed during moldingof the lower frame structure 60 such that it is an integral part of theframe 44.

The frame 44 is thus constructed in this embodiment to enhance theperformance of the track assembly 16 _(i). For example, due to thehollowness of its lower frame structure 60, the frame 44 may bevoluminous yet lightweight, thus helping to contain an overall weight ofthe track assembly 16 _(i). As another example, by being voluminous, thelower frame structure 60 occupies space within the track assembly 16_(i) which would otherwise be available for unwanted ground matter(i.e., mud, rocks, soil, ice, snow, and/or other debris) to accumulatein, and, therefore, helps to reduce a potential for unwanted groundmatter accumulation in the track assembly 16 _(i). As yet anotherexample, the upper frame structure 62 provides a rigid structure whichmay enhance driving precision, while the lower frame structure 60provides a less rigid, more resilient structure which may be beneficialwhen the track assembly 16 _(i) experiences strong impacts in use. Asyet another example, the interwheel guides 70 ₁-70 ₄, the fenders 80₁-80 ₈ and the deflector 75 contribute to improving the performance ofthe endless track 41 and the idler wheels 50 ₁-50 ₁₀.

Although it is configured in a certain manner in this embodiment, theframe 44 may be configured in various other manners in otherembodiments.

For example, while the lower frame structure 60 and the upper framestructure 62 have certain shapes in this embodiment, the lower framestructure 60 and/or the upper frame structure 62 may have various othershapes in other embodiments.

As another example, although in this embodiment the lower framestructure 60 is blow-molded, in other embodiments, the lower framestructure 60 may be manufactured using other manufacturing processes.For example, in some embodiments, the lower frame structure 60 may bemanufactured by a rotational molding (sometimes also referred to as“rotomolding”) process in which a heated mold is filled with materialand then rotated (e.g., about two perpendicular axes) to cause thematerial to disperse and stick to a wall of the mold. As anotherexample, in some embodiments, the lower frame structure 60 may bemanufactured by individually forming two or more pieces and thenassembling these pieces together (e.g., individually forming two halvesof the lower frame structure 60 and then assembling these two halvestogether; individually forming a core of the lower frame structure 60and one or more of the interwheel guides 70 ₁-70 ₄ and the fenders 80 ₂,80 ₃ and then assembling these pieces together; etc.). Such individualforming of two or more pieces may be effected by individually molding(e.g., by an injection or other molding process), extruding, orotherwise forming these two or more pieces. Such assembling may beeffected by welding (e.g., sonic welding), adhesive bonding, using oneor more fasteners (e.g., bolts, screws, nails, etc.), or any othersuitable technique.

As another example, while in this embodiment it is polymeric, in otherembodiments, the nonmetallic material from which the lower framestructure 60 is at least mainly made may another nonmetallic material(e.g., a nonpolymer-matrix composite material).

As another example, while in this embodiment it is nonmetallic, in otherembodiments, material from which the lower frame structure 60 is atleast mainly made may be metallic. For example, in some embodiments, thelower frame structure 60 may be made of aluminum, steel or any othersuitable metal. In such embodiments, the hollowness, the interwheelguides 70 ₁-70 ₄ and the fenders 80 ₁-80 ₈ of the lower frame structure60 may be realized during molding of the lower frame structure 60. Forinstance, this may be achieved by a hydroforming process in whichmetallic material (e.g., an aluminum tube) intended to form the lowerframe structure 60 is placed into a die and a high-pressure hydraulicfluid is used to force the metallic material against the die, therebyforming the lower frame structure 60. This illustrates that, in someembodiments, depending on the material making up the lower framestructure 60, the hollowness, the interwheel guides 70 ₁-70 ₄ and thefenders 80 ₁-80 ₈ of the lower frame structure 60 may be realized usinga fluid-based molding process in which a pressurized fluid (e.g., gas inthe case of a blow-molding process or hydraulic fluid in the case of ahydroforming process) forces the material against a mold to form thelower frame structure 60.

As another example, although in this embodiment it is metallic, in otherembodiments, material from which the upper frame structure 62 is mademay be nonmetallic material. For instance, in some embodiments, theupper frame structure 62 may be at least mainly made of a polymer or apolymer-matrix composite material (e.g., a fiber-reinforced polymer suchas a carbon-fiber-reinforced polymer or glass-fiber-reinforced polymer).

As another example, while in this embodiment they are made of differentmaterials, in other embodiments, the lower frame structure 60 and theupper frame structure 62 may be made of a common (i.e., the same)material. Also, while in this embodiment they are formed separately andthen secured to one another, in other embodiments, the lower framestructure 60 and the upper frame structure 62 may be formed togethersimultaneously such that they are integral with one another (e.g., thelower frame structure 60 and the upper frame structure 62 may be moldedtogether in a common molding process).

As another example, although in this embodiment the interwheel guides 70₁-70 ₄, the fenders 80 ₁-80 ₈ and the deflector 75 are integrally formedduring molding of the frame 44, in other embodiments, one or more of theinterwheel guides 70 ₁-70 ₄, the fenders 80 ₁-80 ₈ and the deflectorguide 75 may be manufactured separately from a core of the frame 44(possibly from materials different from that of the core of the frame44) and affixed (e.g., welded, adhesively bonded, fastened using one ormore fasteners, etc.) to the core of the frame 44.

While in this embodiment the track assembly 16 _(i) is part of an ATV,in other embodiments, a track assembly, including a frame, constructedaccording to principles discussed herein may be used as part of trackassemblies of other types of off-road vehicles. For example, in someembodiments, as shown in FIG. 26, a frame 144 constructed according toprinciples discussed herein may be used as part of a track assembly 116of a snowmobile 110.

The ATV 10 and the snowmobile 110 considered above are examples ofrecreational vehicles. While they can be used for recreational purposes,such recreational vehicles may also be used for utility purposes in somecases. Also, while these examples pertain to recreational vehicles, atrack assembly, including a frame, constructed according to principlesdiscussed herein may be used as part of track assemblies of off-roadvehicles other than recreational ones.

Although various embodiments and examples have been presented, this wasfor the purpose of describing, but not limiting, the invention. Variousmodifications and enhancements will become apparent to those of ordinaryskill in the art and are within the scope of the invention, which isdefined by the appended claims.

1. A track assembly for traction of an off-road vehicle, the trackassembly comprising: a plurality of track-contacting wheels comprising:a drive wheel; and a plurality of idler wheels spaced apart in alongitudinal direction of the track assembly; an endless track disposedaround the track-contacting wheels and comprising an inner side facingthe track-contacting wheels and a ground-engaging outer side forengaging the ground, the drive wheel being rotatable to impart motion ofthe endless track, the idler wheels contacting a bottom run of theendless track; and a frame supporting the idler wheels, the framecomprising a nonmetallic hollow frame structure.
 2. The track assemblyclaimed in claim 1, wherein the nonmetallic hollow frame structure is apolymeric hollow frame structure.
 3. The track assembly claimed in claim2, wherein the polymeric hollow frame structure is a blow-moldedpolymeric hollow frame structure.
 4. The track assembly claimed in claim1, wherein the nonmetallic hollow frame structure comprises a wallforming a hollow interior and having a thickness of at least 1 mm. 5.The track assembly claimed in claim 1, wherein the nonmetallic hollowframe structure comprises a wall forming a hollow interior and having athickness of at least 2 mm.
 6. The track assembly claimed in claim 1,wherein the nonmetallic hollow frame structure is shaped to impedeaccumulation of undesirable ground matter over the nonmetallic hollowframe structure.
 7. The track assembly claimed in claim 1, wherein across-sectional shape of the nonmetallic hollow frame structure changesalong the longitudinal direction of the track assembly.
 8. The trackassembly claimed in claim 1, wherein the nonmetallic hollow framestructure extends at least as high as a given one of the idler wheelssuch that a point of the nonmetallic hollow frame structure aligned witha top of the given one of the idler wheels in the longitudinal directionof the track assembly is located at least as high as the top of thegiven one of the idler wheels.
 9. The track assembly claimed in claim 8,wherein the nonmetallic hollow frame structure extends higher than thegiven one of the idler wheels such that the point of the nonmetallichollow frame structure aligned with the top of the given one of theidler wheels in the longitudinal direction of the track assembly islocated higher than the top of the given one of the idler wheels. 10.The track assembly claimed in claim 8, wherein the given one of theidler wheels is a first one of the idler wheels, the nonmetallic hollowframe structure extending at least as high as a second one of the idlerwheels such that a point of the nonmetallic hollow frame structurealigned with a top of the second one of the idler wheels in thelongitudinal direction of the track assembly is located at least as highas the top of the second one of the idler wheels.
 11. The track assemblyclaimed in claim 1, wherein the frame comprises a metallic framestructure extending upwardly from the nonmetallic hollow framestructure.
 12. The track assembly claimed in claim 11, wherein themetallic frame structure comprises a pair of frame members whichconverge upwardly.
 13. The track assembly claimed in claim 1, whereinthe frame is pivotable about a pivot axis.
 14. The track assemblyclaimed in claim 13, wherein the drive wheel is rotatable about an axisof rotation, the pivot axis of the frame corresponding to the axis ofrotation of the drive wheel.
 15. The track assembly claimed in claim 11,wherein the frame is pivotable about a pivot axis, the track assemblycomprising an anti-rotation connector to limit a pivoting movement ofthe track assembly, the anti-rotation connector being connected betweenthe metallic frame structure and a chassis of the off-road vehicle. 16.The track assembly claimed in claim 1, wherein the nonmetallic hollowframe structure comprises an interwheel guide for contacting the bottomrun of the endless track, the interwheel guide being located between afirst one of the idler wheels and a second one of the idler wheels whichare adjacent to one another in the longitudinal direction of the trackassembly.
 17. The track assembly claimed in claim 16, wherein theinterwheel guide comprises a track-contacting surface having a pointlocated, along a widthwise direction of the track assembly, where apoint of a circumferential surface of each of the first one of the idlerwheels and the second one of the idler wheels is located.
 18. The trackassembly claimed in claim 16, wherein the track-contacting surface ofthe interwheel guide is generally parallel to a line tangent to thefirst one of the idler wheels and the second one of the idler wheels.19. The track assembly claimed in claim 16, wherein the interwheel guideis a first interwheel guide, the nonmetallic hollow frame structurecomprising a second interwheel guide for contacting the bottom run ofthe endless track, the second interwheel guide being located between athird one of the idler wheels and a fourth one of the idler wheels thatare adjacent to one another in the longitudinal direction of the trackassembly.
 20. The track assembly claimed in claim 1, wherein thenonmetallic hollow frame structure comprises a fender adjacent to agiven one of the idler wheels. 21.-66. (canceled)